History

The ABO blood group system is widely credited to have been founded by the Austrian scientist Karl Landsteiner, who found three different blood types in 1900. Ethnic studies did show different blood group distributions across the world (e.g. Asian people having a higher percentage of Type B). This fact was used by early Nazis to further ideas of supremacy over different races. Those distortions were debunked before Nazi Germany invoked race laws like the Nuremberg Laws, where the wording "German blood" is figurative for Aryan lineage.

The theory first reached Japan in 1927 in Takeji Furukawa's paper "The Study of Temperament Through Blood Type" in the scholarly journal Psychological Research. He was a professor at Tokyo Women's Teacher's School. The idea quickly took off with the Japanese public despite his lack of credentials, and the militarist government of the time commissioned a study aimed at breeding the soldiers. The study used no more than ten to twenty people for the investigation. The breeding program therefore ended up with miserable results - most of the army selected by the project lost their lives. In another study, Furukawa compared the distribution of blood types among two different ethnic groups, the Formosans in Taiwan and the Ainu who live in Northeast Asia, especially Hokkaidō. His motivation for the study appears to have derived from a political incident. After the Japanese occupation of Taiwan following Japan's victory over China in 1895, the inhabitants tenaciously resisted their occupiers. Insurgencies in 1930 and in 1931 killed hundreds of Japanese settlers. The purpose of Furukawa's studies was to "penetrate the essence of the racial traits of the Taiwanese, who recently revolted and behaved so cruelly". Based on the finding that 41.2% of a Taiwanese sample had type O blood, he assumed that their rebelliousness was genetically determined. The reasoning was supported by the fact that among the Ainu, whose temperament was characterized as submissive, only 23.8% had type O. In conclusion, Furukawa suggested that the Taiwanese should intermarry more with the Japanese in order to reduce the number of individuals with type O blood.

The craze faded in the 1930s as its unscientific basis became evident. It was revived in the 1970s with a book by Masahiko Nomi, a lawyer and broadcaster with no medical background. Nomi's work was largely uncontrolled and anecdotal, and the methodology of his conclusions is unclear. Because of this he has been heavily assailed by the Japanese psychological community, although his books are phenomenally popular.

Current popularity

Discussion of blood types is widely popular in women's magazines as a way to gauge relationship compatibility with a potential or current partner. Morning television shows feature blood type horoscopes, and similar horoscopes are published daily in newspapers. Though there is not a proven correlation between blood type and personality, it has still remained in the many matchmaking services that cater to blood type. In this way, it is similar to the use of astrological signs in the west, which is also popular in Japan. Asking about a blood type is common and it is often a surprise if a foreigner does not know his or her own blood type.

Many idols, tarento and other Japanese celebrities include a blood type statistic in their profiles, in addition to other facts such as their hobbies and star sign.

For a hilarious example in Korean pop culture, see Episode 9 of My Name Is Kim Sam Soon (the US English-subtitled version is called My Lovely Sam Soon). Watch Sam Soon analyze how love interest Jin Heon will deal with the dilemma of being stuck in the men's bathroom without toilet paper, based on what his blood type might be. Just how it was that Jin Heon managed to escape the uncomfortable situation remains a tantalizing mystery until Episode 13.